001 /*
002 * Copyright 2001-2006 Stephen Colebourne
003 *
004 * Licensed under the Apache License, Version 2.0 (the "License");
005 * you may not use this file except in compliance with the License.
006 * You may obtain a copy of the License at
007 *
008 * http://www.apache.org/licenses/LICENSE-2.0
009 *
010 * Unless required by applicable law or agreed to in writing, software
011 * distributed under the License is distributed on an "AS IS" BASIS,
012 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
013 * See the License for the specific language governing permissions and
014 * limitations under the License.
015 */
016 package org.joda.time;
017
018 import org.joda.time.base.BaseSingleFieldPeriod;
019 import org.joda.time.field.FieldUtils;
020 import org.joda.time.format.ISOPeriodFormat;
021 import org.joda.time.format.PeriodFormatter;
022
023 /**
024 * An immutable time period representing a number of months.
025 * <p>
026 * <code>Months</code> is an immutable period that can only store months.
027 * It does not store years, days or hours for example. As such it is a
028 * type-safe way of representing a number of months in an application.
029 * <p>
030 * The number of months is set in the constructor, and may be queried using
031 * <code>getMonths()</code>. Basic mathematical operations are provided -
032 * <code>plus()</code>, <code>minus()</code>, <code>multipliedBy()</code> and
033 * <code>dividedBy()</code>.
034 * <p>
035 * <code>Months</code> is thread-safe and immutable.
036 *
037 * @author Stephen Colebourne
038 * @since 1.4
039 */
040 public final class Months extends BaseSingleFieldPeriod {
041
042 /** Constant representing zero months. */
043 public static final Months ZERO = new Months(0);
044 /** Constant representing one month. */
045 public static final Months ONE = new Months(1);
046 /** Constant representing two months. */
047 public static final Months TWO = new Months(2);
048 /** Constant representing three months. */
049 public static final Months THREE = new Months(3);
050 /** Constant representing four months. */
051 public static final Months FOUR = new Months(4);
052 /** Constant representing five months. */
053 public static final Months FIVE = new Months(5);
054 /** Constant representing six months. */
055 public static final Months SIX = new Months(6);
056 /** Constant representing seven months. */
057 public static final Months SEVEN = new Months(7);
058 /** Constant representing eight months. */
059 public static final Months EIGHT = new Months(8);
060 /** Constant representing nine months. */
061 public static final Months NINE = new Months(9);
062 /** Constant representing ten months. */
063 public static final Months TEN = new Months(10);
064 /** Constant representing eleven months. */
065 public static final Months ELEVEN = new Months(11);
066 /** Constant representing twelve months. */
067 public static final Months TWELVE = new Months(12);
068 /** Constant representing the maximum number of months that can be stored in this object. */
069 public static final Months MAX_VALUE = new Months(Integer.MAX_VALUE);
070 /** Constant representing the minimum number of months that can be stored in this object. */
071 public static final Months MIN_VALUE = new Months(Integer.MIN_VALUE);
072
073 /** The parser to use for this class. */
074 private static final PeriodFormatter PARSER = ISOPeriodFormat.standard().withParseType(PeriodType.months());
075 /** Serialization version. */
076 private static final long serialVersionUID = 87525275727380867L;
077
078 //-----------------------------------------------------------------------
079 /**
080 * Obtains an instance of <code>Months</code> that may be cached.
081 * <code>Months</code> is immutable, so instances can be cached and shared.
082 * This factory method provides access to shared instances.
083 *
084 * @param months the number of months to obtain an instance for
085 * @return the instance of Months
086 */
087 public static Months months(int months) {
088 switch (months) {
089 case 0:
090 return ZERO;
091 case 1:
092 return ONE;
093 case 2:
094 return TWO;
095 case 3:
096 return THREE;
097 case 4:
098 return FOUR;
099 case 5:
100 return FIVE;
101 case 6:
102 return SIX;
103 case 7:
104 return SEVEN;
105 case 8:
106 return EIGHT;
107 case 9:
108 return NINE;
109 case 10:
110 return TEN;
111 case 11:
112 return ELEVEN;
113 case 12:
114 return TWELVE;
115 case Integer.MAX_VALUE:
116 return MAX_VALUE;
117 case Integer.MIN_VALUE:
118 return MIN_VALUE;
119 default:
120 return new Months(months);
121 }
122 }
123
124 //-----------------------------------------------------------------------
125 /**
126 * Creates a <code>Months</code> representing the number of whole months
127 * between the two specified datetimes. This method corectly handles
128 * any daylight savings time changes that may occur during the interval.
129 *
130 * @param start the start instant, must not be null
131 * @param end the end instant, must not be null
132 * @return the period in months
133 * @throws IllegalArgumentException if the instants are null or invalid
134 */
135 public static Months monthsBetween(ReadableInstant start, ReadableInstant end) {
136 int amount = BaseSingleFieldPeriod.between(start, end, DurationFieldType.months());
137 return Months.months(amount);
138 }
139
140 /**
141 * Creates a <code>Months</code> representing the number of whole months
142 * between the two specified partial datetimes.
143 * <p>
144 * The two partials must contain the same fields, for example you can specify
145 * two <code>LocalDate</code> objects.
146 *
147 * @param start the start partial date, must not be null
148 * @param end the end partial date, must not be null
149 * @return the period in months
150 * @throws IllegalArgumentException if the partials are null or invalid
151 */
152 public static Months monthsBetween(ReadablePartial start, ReadablePartial end) {
153 if (start instanceof LocalDate && end instanceof LocalDate) {
154 Chronology chrono = DateTimeUtils.getChronology(start.getChronology());
155 int months = chrono.months().getDifference(
156 ((LocalDate) end).getLocalMillis(), ((LocalDate) start).getLocalMillis());
157 return Months.months(months);
158 }
159 int amount = BaseSingleFieldPeriod.between(start, end, ZERO);
160 return Months.months(amount);
161 }
162
163 /**
164 * Creates a <code>Months</code> representing the number of whole months
165 * in the specified interval. This method corectly handles any daylight
166 * savings time changes that may occur during the interval.
167 *
168 * @param interval the interval to extract months from, null returns zero
169 * @return the period in months
170 * @throws IllegalArgumentException if the partials are null or invalid
171 */
172 public static Months monthsIn(ReadableInterval interval) {
173 if (interval == null) {
174 return Months.ZERO;
175 }
176 int amount = BaseSingleFieldPeriod.between(interval.getStart(), interval.getEnd(), DurationFieldType.months());
177 return Months.months(amount);
178 }
179
180 /**
181 * Creates a new <code>Months</code> by parsing a string in the ISO8601 format 'PnM'.
182 * <p>
183 * The parse will accept the full ISO syntax of PnYnMnWnDTnHnMnS however only the
184 * months component may be non-zero. If any other component is non-zero, an exception
185 * will be thrown.
186 *
187 * @param periodStr the period string, null returns zero
188 * @return the period in months
189 * @throws IllegalArgumentException if the string format is invalid
190 */
191 public static Months parseMonths(String periodStr) {
192 if (periodStr == null) {
193 return Months.ZERO;
194 }
195 Period p = PARSER.parsePeriod(periodStr);
196 return Months.months(p.getMonths());
197 }
198
199 //-----------------------------------------------------------------------
200 /**
201 * Creates a new instance representing a number of months.
202 * You should consider using the factory method {@link #months(int)}
203 * instead of the constructor.
204 *
205 * @param months the number of months to represent
206 */
207 private Months(int months) {
208 super(months);
209 }
210
211 /**
212 * Resolves singletons.
213 *
214 * @return the singleton instance
215 */
216 private Object readResolve() {
217 return Months.months(getValue());
218 }
219
220 //-----------------------------------------------------------------------
221 /**
222 * Gets the duration field type, which is <code>months</code>.
223 *
224 * @return the period type
225 */
226 public DurationFieldType getFieldType() {
227 return DurationFieldType.months();
228 }
229
230 /**
231 * Gets the period type, which is <code>months</code>.
232 *
233 * @return the period type
234 */
235 public PeriodType getPeriodType() {
236 return PeriodType.months();
237 }
238
239 //-----------------------------------------------------------------------
240 /**
241 * Gets the number of months that this period represents.
242 *
243 * @return the number of months in the period
244 */
245 public int getMonths() {
246 return getValue();
247 }
248
249 //-----------------------------------------------------------------------
250 /**
251 * Returns a new instance with the specified number of months added.
252 * <p>
253 * This instance is immutable and unaffected by this method call.
254 *
255 * @param months the amount of months to add, may be negative
256 * @return the new period plus the specified number of months
257 * @throws ArithmeticException if the result overflows an int
258 */
259 public Months plus(int months) {
260 if (months == 0) {
261 return this;
262 }
263 return Months.months(FieldUtils.safeAdd(getValue(), months));
264 }
265
266 /**
267 * Returns a new instance with the specified number of months added.
268 * <p>
269 * This instance is immutable and unaffected by this method call.
270 *
271 * @param months the amount of months to add, may be negative, null means zero
272 * @return the new period plus the specified number of months
273 * @throws ArithmeticException if the result overflows an int
274 */
275 public Months plus(Months months) {
276 if (months == null) {
277 return this;
278 }
279 return plus(months.getValue());
280 }
281
282 //-----------------------------------------------------------------------
283 /**
284 * Returns a new instance with the specified number of months taken away.
285 * <p>
286 * This instance is immutable and unaffected by this method call.
287 *
288 * @param months the amount of months to take away, may be negative
289 * @return the new period minus the specified number of months
290 * @throws ArithmeticException if the result overflows an int
291 */
292 public Months minus(int months) {
293 return plus(FieldUtils.safeNegate(months));
294 }
295
296 /**
297 * Returns a new instance with the specified number of months taken away.
298 * <p>
299 * This instance is immutable and unaffected by this method call.
300 *
301 * @param months the amount of months to take away, may be negative, null means zero
302 * @return the new period minus the specified number of months
303 * @throws ArithmeticException if the result overflows an int
304 */
305 public Months minus(Months months) {
306 if (months == null) {
307 return this;
308 }
309 return minus(months.getValue());
310 }
311
312 //-----------------------------------------------------------------------
313 /**
314 * Returns a new instance with the months multiplied by the specified scalar.
315 * <p>
316 * This instance is immutable and unaffected by this method call.
317 *
318 * @param scalar the amount to multiply by, may be negative
319 * @return the new period multiplied by the specified scalar
320 * @throws ArithmeticException if the result overflows an int
321 */
322 public Months multipliedBy(int scalar) {
323 return Months.months(FieldUtils.safeMultiply(getValue(), scalar));
324 }
325
326 /**
327 * Returns a new instance with the months divided by the specified divisor.
328 * The calculation uses integer division, thus 3 divided by 2 is 1.
329 * <p>
330 * This instance is immutable and unaffected by this method call.
331 *
332 * @param divisor the amount to divide by, may be negative
333 * @return the new period divided by the specified divisor
334 * @throws ArithmeticException if the divisor is zero
335 */
336 public Months dividedBy(int divisor) {
337 if (divisor == 1) {
338 return this;
339 }
340 return Months.months(getValue() / divisor);
341 }
342
343 //-----------------------------------------------------------------------
344 /**
345 * Returns a new instance with the months value negated.
346 *
347 * @return the new period with a negated value
348 * @throws ArithmeticException if the result overflows an int
349 */
350 public Months negated() {
351 return Months.months(FieldUtils.safeNegate(getValue()));
352 }
353
354 //-----------------------------------------------------------------------
355 /**
356 * Is this months instance greater than the specified number of months.
357 *
358 * @param other the other period, null means zero
359 * @return true if this months instance is greater than the specified one
360 */
361 public boolean isGreaterThan(Months other) {
362 if (other == null) {
363 return getValue() > 0;
364 }
365 return getValue() > other.getValue();
366 }
367
368 /**
369 * Is this months instance less than the specified number of months.
370 *
371 * @param other the other period, null means zero
372 * @return true if this months instance is less than the specified one
373 */
374 public boolean isLessThan(Months other) {
375 if (other == null) {
376 return getValue() < 0;
377 }
378 return getValue() < other.getValue();
379 }
380
381 //-----------------------------------------------------------------------
382 /**
383 * Gets this instance as a String in the ISO8601 duration format.
384 * <p>
385 * For example, "P4M" represents 4 months.
386 *
387 * @return the value as an ISO8601 string
388 */
389 public String toString() {
390 return "P" + String.valueOf(getValue()) + "M";
391 }
392
393 }